► In this thesis a sample cell has been developed which is capable of measuring the structural variations of piezoelectric ceramic materials using low-energy X-ray scattering…
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▼ In this thesis a sample cell has been developed which is capable of measuring the structural variations of piezoelectric ceramic materials using low-energy X-ray scattering techniques in reflection geometry during the application of an electric field, while simultaneously collecting macroscopic strain data using a linear displacement sensor. The results show that the macroscopic strain measured using the cell can be directly correlated with the microscopic response of the material obtained from diffraction data.The electro-mechanical coupling mechanisms in polycrystalline ferroelectric materials including a soft PZT and a lead-free 0.9375(Bi1/2Na1/2)TiO3-0.0625BaTiO3 (BNT-6.25BT) have been contrasted using surface sensitive in situ low-energy (12.4 keV) and bulk sensitive in situ high-energy (73 keV) synchrotron XRD during the application of electric fields. The results allow a direct comparison of the microscopic responses between the bulk grains constrained in three dimensions and the surface grains which have one dimension of mechanical freedom. It is shown that for both PZT and BNT-6.25BT the intrinsic lattice strains and extrinsic non-180° domain switching strains are larger at the surface than those in the bulk of the samples. The property difference is believed to result from the fact that surface grains are not constrained in three dimensions and consequently domain reorientation and lattice expansion in surface grains along the field direction occur more freely. The magnitude of the property difference between the surface and bulk is higher for PZT than for BNT-6.25BT due to the magnitude of anisotropy in the strain mechanism. The comparison of the results from different methods reveals that the grain-to-grain interactions have a significant influence on the electric-field-induced electro-mechanical responses in bulk polycrystalline ferroelectrics.The structure-property relationships in a series of BNT-BT solid solutions with the BT content ranging from 5 mol% to 8 mol% in 0.25 mol% steps were also studied using in situ high-energy synchrotron XRD. This fine compositional deference helps to make a comprehensive picture of field-induced phases particularly in the “pseudo-cubic” region of the phase diagram. Unipolar stress cycling with a maximum stress of approximately 600 MPa and bipolar electric-field cycling with a maximum field of 5 kV/mm were applied in two separate experiments. In the as-processed state, BNT-5BT exhibited rhombohedral crystallographic symmetry, while the rest of BNT-xBT compositions (5.25 ≤ x ≤ 8) exhibited the pseudo-cubic symmetry. During the application of stress and electric field in two separate experiments, lower BT content samples (x = 5.25 and 5.5) tended to transform to rhombohedral symmetry, while the compositions with higher BT contents (7 ≤ x ≤ 8) tended to transform to tetragonal symmetry. Compositions between these (5.5 < x <7) tended to transform to mixed tetragonal-rhombohedral phase symmetry. The results show that the stress and electric-field-induced phase…
Advisors/Committee Members: Daniels, John, MaterialsScience & Engineering, Faculty of Science, UNSW.

► Bismuth ferrite, BiFeO3, is both a piezoelectric and multiferroic material with coupled ferroelectricity, ferroelasticity and antiferromagnetism, which can significantly improve the functional capabilities of devices.…
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▼ Bismuth ferrite, BiFeO3, is both a piezoelectric and multiferroic material with coupled ferroelectricity, ferroelasticity and antiferromagnetism, which can significantly improve the functional capabilities of devices. There are also other desirable properties of bismuth ferrite, including the absence of lead and high Neel and Curie temperatures well above room temperature. Additionally, it displays conductive ferroelectric domain walls that have applications in novel electronic applications. In this thesis, specialised solid state synthesis techniques were used to fabricate phase-pure polycrystalline BiFeO3 ceramics. The macroscopic dielectric and piezoelectric properties were studied and their structural origins were explored using in situ synchrotron X-ray and neutron diffraction. Firstly, the field-dependent nonlinearity of macroscopic strains under sub-coercive field cycling was studied using in situ X-ray diffraction, coupled with measurements of the macroscopic strain. This was followed by studying the Maxwell-Wagner frequency dispersion of macroscopic piezoelectric coefficient and the microscopic strain mechanism contributions via in situ sub-coercive field application. It was found that the domain wall motion and lattice strain decouple from each other. This was shown, by an analytical model, to be due to conductive domain walls. Post-poling relaxation of the macroscopic piezoelectric coefficient and domain texture was also investigated using an ex situ method and in situ synchrotron X-ray diffraction. The phenomenon is ascribed to defect dipoles in the system. Lastly, the coupling of antiferromagnetic and ferroelectric domain texture in the polycrystalline ceramic was studied by in situ neutron diffraction.Based on the results of in situ X-ray diffraction and neutron diffraction with application of electric field, the microscopic contribution to the bulk response and multiferroic order parameter coupling are studied comprehensively. These data are expected to provide valuable information for improving its piezoelectric and multiferroic properties in future studies.
Advisors/Committee Members: Daniels, John, MaterialsScience & Engineering, Faculty of Science, UNSW.

► Lead-free piezoelectric materials are likely to be needed in the near future to replace lead-based materials in applications due to regulatory, health and safety issues.…
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▼ Lead-free piezoelectric materials are likely to be needed in the near future to replace lead-based materials in applications due to regulatory, health and safety issues. Local atomic structural disorder in these materials is suspected to be partially responsible for the functional properties. Therefore, the local structures in promising materials must first be elucidated in order for the future design of high performance lead-free piezoelectrics.Computer simulations have been carried out to model the crystal structure of lead-free pure Na1/2Bi1/2TiO3 (NBT) crystals to explore the effects of occupational disorder in the A-site of the unit cell. “Big-box” models of 30 x 30 x 30 perovskite unit cells were produced using Monte-Carlo simulations. The relationship between neighbouring atoms that occupy the A-site of the perovskite unit cell, known as the correlation coefficient, was simultaneously investigated along the [100], [110] and [111] directions of the crystal structure. Adjusting the correlation coefficient from negative values (Bi-Na or Na-Bi) to positive values (Bi-Bi or Na-Na) along the [100] direction caused changes to the [110] and [111] correlations. However, alterations of [110] and [111] correlations produced overall correlations of zero in the other two respective directions. The diffuse scattering patterns were calculated for the models and the effects of varying A-site occupancy correlations are evident from the contrasting features within these patterns. Furthermore, the calculated diffuse scattering patterns were compared with patterns from reported models and discrepancies were apparent between the two results.Additionally, diffuse X-ray scattering intensities from a single crystal of 0.96Na1/2Bi1/2TiO3 – 0.04BaTiO3 (NBT-4BT) collected at a temperature of 275 °C were analysed. Two distinct satellite peaks, not previously reported, suggest separate modulations in the crystal structure of 11 Å and 35 Å. Larger quantitative modelling is required to confirm such mechanisms.
Advisors/Committee Members: Daniels, John, MaterialsScience & Engineering, Faculty of Science, UNSW.

► Electroceramic materials are a key component to many modern technologies. The controlled development of crystallographic texture in electroceramics is one way for effectively improving their…
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▼ Electroceramic materials are a key component to many modern technologies. The controlled development of crystallographic texture in electroceramics is one way for effectively improving their properties. The preferred orientation governs various structural and mechanical properties of these materials. Several methods have been demonstrated to texture electroceramic materials, including: 1) templated grain growth (TGG) and 2) the magnetic orientation. This thesis explores experimental techniques for processing of textured electroceramics using electric field particle orientation. It is proposed that the polarization anisotropy of a material may be used to align particles under an external electric field when the particle is free to rotate in a suspension medium. There are several technical difficulties to overcome to achieve such electrical orientation of particles and thus the project description can be described by four major components: 1) calculation of particle poling and reorientation fields, 2) particle preparation, 3) individual particle poling and reorientation, 4) preparation of final textured ceramics. Within this thesis both the calculations of required processing conditions and the production of suitable powders was achieved.BaTiO3 was chosen as a model system as it is one of the most extensively studied ferroelectric materials and can be generated in ceramic form with variable grain size. The use of BaTiO3 for piezoelectric applications is, however, limited due to the small piezoelectric coefficient and temperature instability of response. The texturing method explored however, should be applicable to a wide range of materials and may be of use for the development of future lead-free piezoelectric ceramics.BaTiO3 ceramics with optimum grain sizes of 25µm were processed by adjusting the sintering temperature used. These particles were then separated into particle size distributions with a narrow size width such that each particle has the minimum number of grains within it. When used with a suspension medium with a dielectric constant approximately 21 and a packing density of BT particles of 63%vol. it was found that an external field of 20.54kv/mm was required to first pole the individual particles and then reorient them.Further work is proposed to achieve the final goal of producing a textured electroceramic using the methods outlined in this thesis.
Advisors/Committee Members: Daniels, John, MaterialsScience & Engineering, Faculty of Science, UNSW.

Sabbagh Alvani, M. (2013). Powder processing for the fabrication of electric-field textured electroceramics. (Masters Thesis). University of New South Wales. Retrieved from http://handle.unsw.edu.au/1959.4/54391 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:34905/SOURCE02?view=true

Sabbagh Alvani M. Powder processing for the fabrication of electric-field textured electroceramics. [Internet] [Masters thesis]. University of New South Wales; 2013. [cited 2019 May 25].
Available from: http://handle.unsw.edu.au/1959.4/54391 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:34905/SOURCE02?view=true.

Council of Science Editors:

Sabbagh Alvani M. Powder processing for the fabrication of electric-field textured electroceramics. [Masters Thesis]. University of New South Wales; 2013. Available from: http://handle.unsw.edu.au/1959.4/54391 ; https://unsworks.unsw.edu.au/fapi/datastream/unsworks:34905/SOURCE02?view=true

University of New South Wales

5.
Tang, HuiXiang.
Effect of thermal processing on structure and properties of a magnesium-lithium alloy.

► Ultra-lightweight alloys with high strength, ductility and corrosion resistance are desirable for applications in the automotive, aerospace, biomedical, sporting and electronic goods sectors. Of these…
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▼ Ultra-lightweight alloys with high strength, ductility and corrosion resistance are desirable for applications in the automotive, aerospace, biomedical, sporting and electronic goods sectors. Of these materials, magnesium (Mg) is the lightest (~ 1.74 g/cm3) of the structural metals, significantly lighter than steel, titanium and aluminium alloys. A new class of Mg alloys containing lithium (Li) were first developed by the United States National Aeronautics and Space Administration (NASA) in the 1960s with ultra-low densities (1.33-1.65 g/cm3) that are arguably the most lightweight of the engineering alloys. These alloys can also contain single- and multiple-phase microstructures depending on alloying additions and processing.Binary MgLi alloys have a Li content dependent microstructure: Type I - hexagonal close-packed (HCP) Mg structure (termed α phase) (0 to 5 wt.% Li); Type II - mixed α+β structure where β phase is body-centered cubic (BCC) (5 to 10.3 wt.% Li); and Type III - fully BCC β phase structure (> 10.3 wt.% Li). A new type of MgLi alloy was developed recently that contains (wt.%) Mg-10.95Li-3.29Al-0.59Y. In its near-equilibrium state (hot extruded and air cooled), this alloy has the α+β structure (Type II) and a small volume fraction of intermetallic compounds, such as Al2Y. In this state, the alloy is soft and ductile, but highly susceptible to corrosion. However, this alloy was also capable of generating a unique property profile after further thermal and mechanical processing, i.e. high strength, appreciable ductility and good corrosion resistance (Xu et al., Nature Materials, vol. 14, p. 1229, 2015). Such a property profile was argued to be a result of the formation of both an unusual Li-rich solute nanostructure within the single-phase BCC Mg-rich β matrix and a uniform lithium-carbonate film on the alloy surface.While this MgLi alloy demonstrated an exceptional structural and mechanical (+ corrosion) response to heat treatment, many processing parameters are still not well understood regarding its hardening and softening behaviour. Hence, this thesis focuses on the structural and mechanical response of this MgLi alloy to thermal processing. It was found that the alloy quench-hardened after solution treatment at temperatures greater than 200 °C but age-softened during holding at temperatures as low as room temperature. The unusual Li-rich solute nanostructure that forms in the BCC β matrix of the alloy after water quenching from 400 °C was investigated systematically for understanding if this type of structure was major cause of the considerable quench-hardening and subsequent softening during ageing over a range of temperatures (20 to 220 °C). Here, in-situ high energy synchrotron small-angle and wide-angle X-ray scattering (SAXS/WAXS), in conjunction with conventional X-ray diffraction (XRD) and scanning electron microscopy (SEM), were used for the structural studies, with hardness used mainly for tracking changes in mechanical properties.The…
Advisors/Committee Members: Ferry, Michael, MaterialsScience & Engineering, Faculty of Science, UNSW, Daniels, John, MaterialsScience & Engineering, Faculty of Science, UNSW.

Tang, H. (2017). Effect of thermal processing on structure and properties of a magnesium-lithium alloy. (Doctoral Dissertation). University of New South Wales. Retrieved from http://handle.unsw.edu.au/1959.4/57474

Chicago Manual of Style (16th Edition):

Tang, HuiXiang. “Effect of thermal processing on structure and properties of a magnesium-lithium alloy.” 2017. Doctoral Dissertation, University of New South Wales. Accessed May 25, 2019.
http://handle.unsw.edu.au/1959.4/57474.

MLA Handbook (7th Edition):

Tang, HuiXiang. “Effect of thermal processing on structure and properties of a magnesium-lithium alloy.” 2017. Web. 25 May 2019.

Vancouver:

Tang H. Effect of thermal processing on structure and properties of a magnesium-lithium alloy. [Internet] [Doctoral dissertation]. University of New South Wales; 2017. [cited 2019 May 25].
Available from: http://handle.unsw.edu.au/1959.4/57474.

Council of Science Editors:

Tang H. Effect of thermal processing on structure and properties of a magnesium-lithium alloy. [Doctoral Dissertation]. University of New South Wales; 2017. Available from: http://handle.unsw.edu.au/1959.4/57474

► Portable, in-situ and on-stream X-ray fluorescence (XRF) is widely used in minerals industry applications to analyse materials with little or no sample preparation. These XRF…
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▼ Portable, in-situ and on-stream X-ray fluorescence (XRF) is widely used in minerals industry applications to analyse materials with little or no sample preparation. These XRF techniques have been found particularly useful for measuring the concentrations of precious and base metal such as gold, platinum, nickel and copper in mineral slurries. The consequence of measuring mineral samples in slurry form is that physical sample effects can limit the accuracy of XRF analysis. This thesis describes two different approaches for improving the XRF analysis of in-situ slurries: thorough characterisation of heavy element L-shell spectra for improved spectral fitting, and the development of a particle size effect correction technique.L-shell X-ray spectra have been measured for 8 elements with atomic numbers between 68 and 79, and the measured line intensity ratios and total subshell intensity ratios are compared to existing theoretical and experimental values. The spectra were carefully fitted to determine line energies and intensities, accounting for Lorentzian line broadening, Compton scattering, incomplete charge collection and the silicon escape effect. A Monte Carlo approach was used to calculate geometry, attenuation and detector efficiency corrections. Up to 15 line intensity ratios and total L1/L3 and L2/L3 subshell intensity ratios are reported for each element. Substantial disagreement is found in both magnitude and trend with atomic number when compared to theory. The measured results are used to predict the errors introduced during elemental composition determination using theoretical basis-function fitting when measured XRF spectra are analysed with incorrect theoretical X-ray emission intensities.The intensity of characteristic fluorescent radiation from mineral phases in particulate materials such as slurries decreases as the particle size of the ore being measured increases. The particle size effect can lead to significant analysis errors, but is usually ignored in on-stream applications where there is limited control over the particle size. This thesis describes measurements of the particle size effect for copper and iron powders in a weakly absorbing matrix. The measured results are compared to a theoretical model and Monte Carlo simulations. A preliminary correction method involving measurements using dual exciting radiation energies is discussed and evaluated using measured and simulated data.
Advisors/Committee Members: Tickner, James, CSIRO, Chrysos, Sahajwalla, Veena, MaterialsScience & Engineering, Faculty of Science, UNSW, Daniels, John, MaterialsScience & Engineering, Faculty of Science, UNSW.

► Piezoelectric ceramics are used in a wide range of technologies due to their ability to couple mechanical and electrical energy. These materials have traditionally been…
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▼ Piezoelectric ceramics are used in a wide range of technologies due to their ability to couple mechanical and electrical energy. These materials have traditionally been made from compositions in the PbZrO3–PbTiO3 system, which has raised environmental concerns and driven developments towards lead-free alternatives. Such developments have been based around locating compositions at Morphotropic phase boundaries as these compositions tend to achieve the highest strain. Locating such compositions is relatively simple in binary systems, but becomes exceedingly more difficult in ternary systems.This project used combinatorial methods to rapidly synthesise and outline phase boundaries in the two ternary systems (Bi0.5Na0.5TiO3)x(BaTiO3)y(SrTiO3)1‒x‒y (BNT-BT-ST) with x ≥ 0.68 and (BiFeO3)x(Bi0.5K0.5TiO3)y(Bi0.5Na0.5TiO3)1‒x‒y (BF-BKT-BNT) with 0.43 ≤ x ≤ 0.75. Scanning synchrotron x-ray powder diffraction was used to determine the long-range average structure at room and elevated temperatures, whilst x-ray Pair Distribution Function (PDF) analysis determined the short-range local-scale distortions.The rhombohedral – cubic phase boundaries were difficult to locate due to small amounts of observable peak splitting, particularly in the high-energy diffraction data. A new technique was developed, which was the weighted parametric Rietveld refinement, where a tan-1 function was applied to the scale factor. This narrows down the refinable parameters to a single quantity, being the phase boundary composition. In both ternary systems this method effectively outlined phase boundaries that had not been established previously.The thermal stability of these materials is very important for device implementation and could be assessed from the temperature dependent diffraction data. The shift in the phase boundaries with temperature indicated that phase boundary compositions in the BF-BKT-BNT system show potential for variable temperature applications, whilst those in the BNT-BT-ST system would be unsuitable.To assess the structural transitions occurring from the short-range local structure to the long-range average structure, box-car refinements were conducted on the PDF data. In both systems, local rhombohedral distortions were observed across all compositions. The BNT-BT-ST system also showed short-range tetragonal distortions for selected compositions, whilst the BF-BKT-BNT system did not.These methods have proven effective at rapidly determining large amounts of structural information that can be used for engineering high performance lead-free piezoelectrics.
Advisors/Committee Members: Daniels, John, MaterialsScience & Engineering, Faculty of Science, UNSW, Standard, Owen, MaterialsScience & Engineering, Faculty of Science, UNSW.

► Piezoelectric ceramics find a wide range of applications in advanced technological fields. Most of the currently used piezoelectric ceramics contain lead (Pb). Environmental concerns and…
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▼ Piezoelectric ceramics find a wide range of applications in advanced technological fields. Most of the currently used piezoelectric ceramics contain lead (Pb). Environmental concerns and limitations in high-temperature performances of market leading Pb(Zr,Ti)O3 has spurred the field of lead-free electroceramics research. Compositions based on Bi1/2Na1/2TiO3, Na1/2K1/2NbO3, BiFeO3 and BaTiO3 have long been considered as candidates to replace lead containing piezoelectric ceramics. Although lead-free compositions based on these systems exhibit electromechanical properties for potential device application, further enhancement of properties and reliability is required. To achieve this, extensive knowledge of structure- property relationships at multiple length scales, especially during the actuation condition is essential. However, systematic studies of the multi- length-scale structural contributions (lattice deformation, domain wall motion, phase transformations) to the field-induced strain in lead-free electroceramics are lacking.To understand the microscopic origin of strain in lead-free electroceramics several compositions have been studied using in situ high-energy x-ray diffraction. Their microscopic strain response has been elucidated under electric field. Strain contributions have been analysed for each system and have been correlated with their macroscopic properties.The first material was a ceramic/ceramic composite of particulate phase 0.93(Bi1/2Na1/2)TiO3-0.07BaTiO3 and matrix phase 0.92(Bi1/2Na1/2)TiO3-0.06BaTiO3-0.02(Na1/2K1/2NbO3). Under applied electric field, this material system showed that the local response of the particulate phase can be used to tailor bulk material properties. A microscopic strain mechanism in ceramic/ceramic composite system was proposed on the basis of these diffraction studies.A microscopic strain mechanism in ceramic/ceramic composite system was proposed on the basis of these diffraction studies. Domain switching in a core-shell BaTiO3-KNbO3 piezoelectric ceramics has also been investigated. The core-shell BT-KN has been shown to exhibit remarkably large reversible domain switching during the application of electric fields.Electromechancial coupling behavior in bulk BiFeO3 has been quantified from diffraction data. The strain mechanism has been contrasted with thin-film BiFeO3. Interestingly, despite the different mechanism, rhombohedral bulk BiFeO3 ceramic can exhibit a similar strain/field ratio to thin-film BiFeO3. This comparative study of strain responses will enable the research field to focus on identified important structural aspects that are essential to improve piezoelectric properties in future lead-free systems.
Advisors/Committee Members: Daniels, John, MaterialsScience & Engineering, Faculty of Science, UNSW, Hoffman, Mark, MaterialsScience & Engineering, Faculty of Science, UNSW.